1. Field of the Invention
The present invention relates to a network system including a switch device and a plurality of communication terminals. The switch device receives a packet at one port thereof and transmits the packet from another port corresponding to a destination of the packet. The communication terminals are connected to the ports of the switch device respectively to transmit and receive packets between the communication terminals through the switch device.
2. Description of the Related Art
A network system such as a LAN includes a switch device which has a plurality of ports and a plurality of communication terminals which are connected to the ports of the switch device. For example, the network system may use a switch device including a plurality of ports based on IEEE802.3. Such a switch device complies with 10Base-T, 100Base-TX, 1000Base-T, or the like specified in IEEE802.3 (for example, see “IEEE Std 802.3-2005, IEEE Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements, Part 3: CSMA/CD Access Method and Physical Layer Specifications,” The Institute of Electrical and Electronics Engineers, Incorporated, 2005).
When a communication terminal is connected to a port of the switch device, the switch device determines a communication speed, a communication direction (full or half duplex), and the like for communication with the connected communication terminal through auto-negotiation or the like as specified in IEEE802.3. Then, the switch device transmits or receives the packet to and from the connected communication terminal. When a packet has been received from the communication terminal, the switch device temporarily stores the packet in a buffer unit or the like. The switch device then determines a port, from which the packet is to be transmitted, from an IP address or the like of a destination written in the packet stored in the buffer unit and then transmits the packet from the determined port.
In the switch device used in the above-described network system, a packet received from a communication terminal is temporarily stored in the buffer unit, a port from which the packet is to be transmitted is decided from an IP address or the like of the destination of the packet, and the packet is then transmitted from the decided port. If the number (or amount) of packets received at the ports of the switch device increases, a bandwidth required to transmit the packets from the ports to the buffer unit increases. If the bandwidth required to transmit packets from the port to the buffer unit increases, the required bandwidth may exceed the transmission capabilities of the switch device. If the bandwidth required to transmit packets exceeds the transmission capabilities of the switch device, packets received from the communication terminal may be lost since no bandwidth guarantee is provided in the switch device.